Prior to the patient undergoing an anaesthetic, a full assessment must be carried out. The preoperative assessment and preparation of the patient has been discussed in detail in Chapter 2. It is important to note the family history, especially of metabolic disease, as certain drugs and anaesthetic agents may affect patients who have a history of malignant hyperthermia. A drug history, including current medications and allergies, should be noted as the interaction of drugs can have serious consequences. A social history, including smoking, alcohol intake and use of illegal drugs, is important to note, as is the use of herbal dietary supplements that are known to produce central nervous system (CNS) stimulation or depression or interact with psychotropic drugs. All these issues can adversely affect the patient’s anaesthetic outcome (Marley, 2005).

The patient assessment must take into consideration the following:

• baseline physiological state

• current and past medical and surgical history

• the planned procedure

• drug sensitivities

• past anaesthetic experience

• psychological make-up (Marley, 2005).

Assessment of the airway

As part of the pre-anaesthetic assessment, it is essential that the anaesthetist predicts airway and intubation difficulties and plans airway management accordingly. Assessment criteria include the following:

• length of incisors—this may impede the introduction of a laryngoscope blade into the mouth

• mobility of cervical spine, length and thickness of neck—to facilitate neck movement during intubation

• the ability to see the soft palate and uvula with the mouth open and tongue protruded, known as the Mallampati score

• the ability to sublux the mandible forward at the temporomandibular joint

• the thyromental distance (less than three fingers)—this is measured from the thyroid notch to the inner border of the mandible when the patient’s head is extended.

Mallampati assessment

The Mallampati test is used to examine the patient’s oral cavity and soft palate visually to predict any possible difficulties with tracheal intubation. It can be conducted during the pre-anaesthetic assessment.Figure 6-1 shows the four classifications. Classes III and VI, which indicate that viewing of the soft palate is difficult or impossible, suggest a higher degree of difficultly with intubation in these patients (Fell & Kirkbride, 2007).

Figure 6-1 Classification of the pharyngeal view when performing the Mallampati test (Aitkenhead et al., 2007, p 285).

Further preoperative considerations

The grading system of the American Society of Anesthesiologists (ASA) was introduced in the 1960s as a description of the physical state of the patient, along with an indication of whether surgery is elective or emergency (Fell & Kirkbride, 2007). The ASA physical status classification system is presented in Table 2-2. The ASA classification of the patient will influence the anaesthetist’s decisions about anaesthetic care and postoperative management. These decisions include whether the patient requires postoperative care in the day surgery unit, inpatient bed, high-dependency unit or adult intensive care unit.

Table 6-2 Intravenous and inhalational anaesthetic agents

After the patient’s history, examination and relevant investigations have been collated, the anaesthetist is able to plan the patient’s care more accurately. The decisions being considered regarding anaesthetic care, pain management and possible blood transfusions should be discussed with the patient and opportunities to ask questions should be made available. Patients should also be given relevant information regarding fasting times and whether to take their regular medications with a sip of water on the day of surgery.

It is important that anaesthetic nurses make themselves familiar with their patient’s history and assessment as soon as patients are admitted into the perioperative environment in order to plan nursing care and to prepare equipment to ensure safe patient outcomes. This will be carried out in conjunction with the anaesthetist to ascertain any special requirements.

Identification and preparation of the patient

The patient is accompanied to the operating suite by a nurse from the ward, who will hand over care of the patient to a member of the perioperative team, usually a nurse in the arrival/waiting area of the operating suite, often termed the ’holding bay’. Both nurses and the patient will participate in completing a preoperative patient checklist (see Figs 2-2 and 2-3) as part of the admission procedure, which will vary according to hospital policy but will include the following:

• identification of the patient, confirming name and medical record number using the patient’s medical history and identification bands

• fasting times

• allergies

• confirmation of consent—the patient confirms procedure, the site and side of surgery; in most hospitals the site of surgery should already be marked by the surgeon, although this may be carried out following admission to the operating suite

• any preoperative medications given.

In addition, it is imperative that an anaesthetic consult is present and complete. Any discrepancies should be noted, reported to the surgical team and rectified before commencement of anaesthesia (ACORN, 2006). The verification of patient details continues throughout each stage of the patient’s care according to local policy.

Prior to the induction of anaesthesia, base line observations of pulse and blood pressure will be taken, electrocardiograph (ECG) monitoring devices and warming devices will be attached, and intravenous (IV) access will be secured. This can be a highly anxious time for the patient and, throughout this time, good communication skills are necessary to explain the procedures to the patient and provide quiet reassurance. Therapeutic touch and other anxiety-reduction measures (e.g. music) may be used.

Types of anaesthetics

Anaesthesia is defined as the ‘loss of the sensations of pain, pressure, temperature and touch in a part of the whole of the body’ (Bryant & Knight, 2007). The main categories of anaesthesia are:

• general

• local infiltration

• regional—spinal and epidural—these can be combined to provide the patient with pain relief in the postoperative period.

• sedation/analgesia.

General anaesthesia

General anaesthesia is a reversible, unconscious state characterised by amnesia, analgesia and suppression of reflexes (DeLamar, 2007). The drugs and gaseous agents used to induce and maintain anaesthesia have a profound physiological effect on body systems, notably the CNS. The area in the CNS that is most affected is the sensory pathways from the thalamus to the cortex, thus depressing conscious thought, motor control, perceptions, memory and sensations. The medullary centres are the final cerebral area to be affected by anaesthesia and unconsciousness occurs, with both respiratory and cardiovascular centres temporarily depressed. These stages of anaesthesia were first described by the American anaesthetist, Arthur Guedel, and are outlined in Table 6-1 (Fell & Kirkbride, 2007).

Table 6-1 Stages of anaesthesia (modified from Guedel)

Pharmacological agents used in general anaesthesia

Intravenous induction agents

IV induction agents are commonly used to induce general anaesthesia because they provide a smoother and more rapid induction than most inhalational agents. Short-acting IV induction agents (e.g. thiopentone, propofol) induce a pleasant sleep, and anaesthesia is maintained for the duration of the surgical procedure by using a combination of oxygen, nitrous oxide and volatile inhalational agents (e.g. sevoflurane). Some anaesthetists may use an IV induction agent as a continuous infusion to maintain anaesthesia, eliminating the need for inhalational agents (Brown & Edwards, 2007).

Inhalational agents

Volatile and gaseous inhalational anaesthetic agents remain popular for the maintenance of anaesthesia, and may be used to induce anaesthesia in paediatrics to avoid the need to insert IV cannulae, which can be traumatic for a child.

Inhalational agents include nitrous oxide, which is colourless, essentially odourless and the only inorganic anaesthetic gas in clinical use. Although it possesses some analgesic properties, it will not maintain narcosis. The addition of a volatile inhalational agent will maintain the patient in an unconscious state.

Volatile agents are liquid at room temperature and administered through a specialised vaporiser that is attached to the anaesthetic machine. Oxygen, which is another gas that must be used in all general anaesthesia, passes through the vaporiser and mixes with the liquid agent, changing the volatile agent into a gas. The mixture is delivered to the patient via the variety of airway and delivery equipment attached to the anaesthetic machine. The percentage of inhalational agents delivered to the patient can be adjusted by the anaesthetist depending on the depth of anaesthesia required. Table 6-2 provides a summary of the IV and inhalational agents used in general anaesthesia.

Adjuncts to general anaesthesia

Table 6-3 provides a summary of the most commonly used adjunct drugs to general anaesthesia. As can be seen from Tables 6-2 and 6-3 , many of the agents used to induce anaesthesia and as adjuncts have a powerful effect on the patient’s cardiovascular and respiratory systems. This requires the anaesthetist and anaesthetic nurse to monitor the patient closely using a variety of invasive and non-invasive haemodynamic monitoring devices (see p 151), as well as observational skills.

Table 6-3 Adjuncts to general anaesthesia

Procedure for general anaesthesia

Anaesthetic preparation and equipment checking

Prior to the commencement of the operating list, it is important that the anaesthetic machine is checked in accordance with the Australian and New Zealand College of Anaesthetists (ANZCA) guidelines by both the anaesthetist and anaesthetic nurse (ANZCA, 2003b). Anaesthetic machines deliver gases and volatile agents to the patient via delivery tubing that attaches to the patient’s airway management equipment (e.g. endotracheal tube). Oxygen, nitrous oxide and air are piped into the operating room via a network of pipes from a central bulk store of gases within the hospital. A pendant attached to the ceiling delivers the gases to the anaesthetic machine through colour-coded tubes (white for oxygen, blue for nitrous oxide). The fixtures for each gas outlet are gas-specific, which is an important safety feature to ensure that the oxygen tubing cannot physically be attached to the nitrous oxide outlet and vice versa. The same feature exists for the back-up gas cylinders attached to the anaesthetic machine. The anaesthetic machine is more than a gas delivery unit. It also contains a range of sophisticated equipment necessary to monitor the patient’s condition throughout the perianaesthesia period (e.g. ECG, oximetry and capnography).

Other preoperative equipment checks include suction, airway equipment, drugs, additional equipment such as infusion pumps, warming devices and all monitoring equipment. These must be available and in working order prior to the patient’s arrival in order to ensure a smooth and safe anaesthesia process for the patient. Figure 6-2 shows an anaesthetic machine complete with monitoring equipment.

Figure 6-2 Anaesthetic machine and monitoring equipment (Rothrock, 2007, p 108). A, BIS monitor display. B, Patient breathing circuit. C, Reservoir (‘breathing’) bag. D, Carbon dioxide absorber. E, Ventilator.F, Integrated ventilator controls, monitor and displays. G, Oxygen auxiliary outlet. H, Oxygen flush valve. I, On/off switch. J, Monitor display and controls for ECG, temperature, blood pressure, pulse oximetry and end-tidal carbon dioxide. K, Flow meters for air. L, Gauges for pipeline and E-tank pressures (air, nitrous oxide, oxygen). M, Flow-through vaporisers (e.g. desflurane, isoflurane, sevoflurane). N, Power surge protector for anaesthesia machine. O, E-cylinder with oxygen.

Induction of anaesthesia

Induction is defined as the administration of a drug or combination of drugs that results in a state of general anaesthesia (Bryant & Knight, 2007). Preoxygenation of the patient may be carried out to avoid transient hypoxaemia, which can occur before the establishment of an effective airway and ventilation.

During induction it is important that the environment is as quiet as possible to facilitate a smooth induction. Extraneous noise from people talking or the instrument and circulating nurses setting up equipment should be minimised during induction (Fell & Kirkbride, 2007).

Establishment of the airway

Once anaesthesia is induced, the patient will proceed through the stages of anaesthesia shown in Table 6-1. The establishment of an airway now becomes a priority. Depending on the type of procedure being undertaken, and the patient’s history and condition, suitable airways will be selected. To understand how artificial airways are used, it is important to review the anatomy of the airway.

The airway is divided into two sections, upper and lower, which are separated at the level of the cricoid cartilage (Chipas et al., 2005). Figure 6-3 shows the anatomy of the upper airway.